Spatial distribution of laser energy and its influence on the stability of extreme narrow keyholes during ultra-high power laser welding

The instability of extremely narrow keyholes is the main challenge in high-power laser welding. In this work, the spatial energy distribution and its influence on the stability of extremely narrow keyholes during ultra-high power laser welding are studied. A multiphase flow model that considers the vapor plume impact and the multiple scattering of laser radiation is built to simulate the topology and downstream wave flow on the keyhole wall. Drastic keyhole fluctuation is due to excessive energy accumulation, which arises from the abnormal wrinkle structures that form on the front keyhole wall. Suppressing the periodic cutting phenomena on the keyhole opening and the hump accumulation effect on the solid-liquid interface help smooth the keyhole surface. Optimized welding processes are obtained, producing fine, closed, and evenly distributed wrinkle structures, and the keyhole stability is correspondingly improved. The simulation results agree well with the experiment.